The rise in complexity and sophistication of electronically controlled devices and systems has been observed to generate a concomitant need for higher quality and very stable sources of power. This need particularly has been witnessed in connection with computer installations and more recently with respect to complex systems wherein loads are suddenly imposed upon a power supply system. The latter systems include, for example, computer aided tomography (CATSCAN) where the abrupt excitation of X-ray generation equipment is called for.
Directly supplied utility power is found to be unacceptable for increasing numbers of these sophisticated equipment installations as a consequence of line power aberrations now typically encountered. These aberrations are manifested as any of a variety of phenomena. For example, out of specification voltages referred to as "sags" are represented as a reduction in rms voltage values over a half cycle interval or more. Where such voltage reductions persist within imporant grids, they are conventionally referred to as "brown outs".
In addition to "sags" as above described, over-voltage excursions referred to as "surges" may be encountered which, in general, are manifested as deviations above nominal rms value lasting for more than a half cycle. These surges generally are encountered in conjunction with load dropping activities.
Subcycle abnormalities also are witnessed in the line power supplies. For example, high voltage, short term spikes may occur. Such excursions have been observed to be caused, inter alia, by lightning strikes or sub-station or capacitor switching by a utility.
Static noise conditions also may be encountered in the line power supplies. Such noise phenomena will include common mode noise occasioned by the operation of electrical equipment in close proximity to the source being relied upon or through load switching. Further, transverse mode noise also may be encountered appearing line-to-line and having similar causation.
When encountered within a computer room environment, the above-cataloged aberrations in line power will have a variety of effects. Line noise may result in data error, unprogrammed jumps and software/data file alterations. Momentary under- and over-voltage generally results in automatic computer power down.
Techniques which have been resorted to by industry in accommodating unreliable power supplies have involved a variety of technical approaches. One such approach looks to the use of regulators, spike suppressors, and the like which function to modify or control the input waveform. Generally, such corrective measures are insufficient in the treatment of adverse line conditions. Regulators, for example, incorporate feedback loops resulting in a slow corrective performance considered inadequate for most applications.
Another utility interactive line conditioner technique has been to employ a generator which is driven by a motor, in turn, powered from the line power supply. For the most part, these generators are driven by induction motors which often are characterized in not achieving sufficiently accurate drive output such that the driven generator will provide adequate frequency performance. Motor-generator drives also have been found to be susceptible to output instabilities when subjected to third harmonic phenomena and the like induced, for example, by load induced shocks or single phasing conditions. The latter conditions occur, for instance, with the occasion of broken lines at the input. It is most desirable to retain a capability for maintaining a quality, sinusoid output even under conditions of extreme unbalance.
Over the recent past, line power conditioners which are structured as polyphase, ferroresonant voltage synthesizers have been successfully introduced to the marketplace. In their elementary form, such synthesizers comprise a regulator which is fashioned as a non-linear saturable transformer in parallel with a capacitor bank and which is supplied from the line source through input inductors. These saturable transformer components and associated capacitors form a ferroresonant circuit wherein the reactive components operate beyond the knee of a conventional magnetization curve. One such improved synthesizer is described in U.S. Pat. No. 4,305,033 by Jeffrey M. Powell assigned in common herewith. The latter synthesizer achieves a highly reliable and stable sinusoid output through the incorporation therewith of odd and even harmonic traps. These traps function only in the presence of transients imposed upon the system to assure stability. Such synthesizers enjoy the advantage of economic construction and efficient performance while remaining immune from adverse characteristics related to stability and reliability which previously had been associated with resonating circuits.
Important improvements in terms of efficiency of operation are achieved with a further improved synthesizer described in U.S. Pat. No. 4,544,877, by Jeffrey M. Powell assigned in common herewith. These efficiencies are achieved by the select location of the capacitors associated with the ferroresonant circuit of a the regulator components of the synthesizer. Additionally, further efficiencies are achieved through a unique design of the input inductor structure.
Where load transients are imposed upon synthesizers, for example, during start-up or the like, the resultant current demands are accommodated for by a rapid adjustment of phase angle toward a lag orientation. This condition obtains until the start-up is accomplished. For some specialized applications requiring a high quality sinusoid output during any first half cycle of start-up demand, for example as seen with some X-ray generators, a stiffened source is desired. Ideally, the utility interactive device used for this type demanding purpose will achieve the highly stable sinusoidal output in the presence of transients generated at the load which is being supplied.